Building standards - (fire safety) external wall systems: consultation analysis

An analysis of the responses to the public consultation on a review of building standards relating to the fire safety of external wall systems to help ensure the safety of people in and around Scotland’s buildings.

5. Part 4 - Consequential Matters – Combustible Exemptions

5.1 Introduction

5.1.1 The Technical Handbook annexes provide a list of A1 and A2 exemptions for reaction to fire. Indeed, in buildings where external wall cladding systems achieve a European Classification A1 or A2, the following products, where used as part of such a wall, need not achieve the same classification:

  • cavity tray
  • any part of a roof (other than a part of a roof pitched at an angle of 70º or more to the horizontal) if that part is connected to an external wall
  • door frames and doors
  • electrical installations
  • insulation and water proofing materials used below ground level
  • intumescent and fire stopping materials where the inclusion of the materials is necessary for compliance with the standards in Section 2 (Fire)
  • membranes
  • seals, gaskets, fixings, sealants and backer rods
  • thermal break materials where the inclusion of the materials is necessary for compliance with the standards in Section 6 (Energy), or
  • window frames and glass.

5.1.2 This list had raised questions about the combustibility of other penetrations through the external wall that are not included e.g. balanced flue liners, drainage and overflow pipes, ventilation extract ducts etc.

5.2 Question 4 – Amendment to List of Exemptions

5.2.1 Question 4 was concerned with the current list of exemptions and asked if the list should be amended to include other penetrations e.g. cavity wall vents, boiler condensate pipes, drainage and overflow pipes, ventilation extract ducts, balanced flue liners etc.

5.2.2 Table 7 below shows whether respondents agreed with the proposal to amend the current list of exemptions to include other penetrations. Responses were broadly split across the three answers of yes, no and unsure, with slightly more respondents (29 respondents or 39%) supporting the proposal than disagreeing with the proposal (22 respondents or 30%). There was also a relatively large proportion of respondents (31%) who were unsure about the proposal.

5.2.3 The proposal was supported by respondents across all categories with the majority of consultancy and local authority respondents agreeing with the proposal. Respondents in the other categories were more evenly distributed across the different answers.

Table 7: Do you think that the current list of exemptions above should be amended to include other penetrations e.g. cavity wall vents, boiler condensate pipes, drainage and overflow pipes, ventilation extract ducts, balanced flue liners?
Yes No Unsure Not Answered Total
Construction Industry 3 1 2 - 6
Consultancy 4 1 2 - 7
Individuals 7 10 5 - 22
Local Authorities 5 1 2 - 8
Manufacturers 2 2 3 - 7
Other 3 3 3 - 9
Research Estab./Fire Test House 1 - 1 - 1
Trade Association 4 4 5 2 15
Total 29 22 23 2 76
% respondents answering question 39 30 31 100

5.2.4 There were 56 comments made in response to this question. Responses are considered separately for those agreeing and those disagreeing with the quantitative part of the question.

Agreeing with the Proposal

Examples to be Included in the List of Exemptions

5.2.5 Many respondents agreeing with the proposal offered suggestions on the products which should be included in the list of exemptions. Suggestions were made by all response categories (except manufacturers) and include:

  • Combustible materials used for weep ventilation, vent ducts, flues etc. Weep vents are usually required with the cavity tray and should be included with the cavity tray.
  • Openings such as cavity wall vents and single ducts that penetrate the non-combustible wall should be allowed as they pose a limited risk to the overall system.
  • Laminated glass as it is exempt[12] and commonly used on balconies and spandrel panels.
  • Combustible rain guards as they pose a limited risk to the overall system.
  • Flue liners, drainage and overflow pipes, ventilation extract ducts and outlet terminals were mentioned by a few respondents.
  • Insect meshes (installed at the top of openings in external walls) as they usually present a low fire risk due to the small quantity of combustible material and there is no wall above for fire to spread vertically.
  • Cavity wall vents and subfloor vents as the industry standard solution is made from combustible material. Cavity wall vents were identified by a few respondents as unlikely to increase fire risk. However, it was suggested there could be challenges based on their design such that these exemptions should be subject to review by following a fire safety engineered approach i.e. a fire risk assessment should be conducted by a competent fire engineer at the time of the design phase and during the construction phase.
  • Soil stack and overflow pipes providing that fire stopping is used where required in the technical handbooks.
  • Ventilation extract ducts with fire stopping used where required in the technical handbooks.
  • Plastic air bricks as they contribute relatively little to the heat output or surface spread of flame in the event of a fire in an external wall.
  • Fan and duct covers for the same reason as plastic air bricks above.

5.2.6 It was suggested that it would be practical to put limits on the maximum dimensions of these service penetrations going through the external envelope, particularly for items which can vary significantly in size e.g. ventilation extract ducts. Also products such as drainage pipes that run the height of the building should not be exempt.

5.2.7 A few respondents suggested changes to the wording of the existing list of exemptions which are shown in bold below:

  • "seals, gaskets, fixings, sealants and backer rods and similar materials"
  • "Insulation and water proofing materials used below ground level" should be adjusted to "below damp-proof course (DPC) level" as many A1 or A2 mineral wool type insulations are not suitable for use below DPC line.

Policy and Clarity

5.2.8 Several comments were received which related to the clarity of policy and guidance. One comment questioned whether there needs to be an exhaustive list of exemptions or whether clarity on policy intent or application is required. Specific reference was made about the clarity of intent of the guidance for certain heating industry products whilst ensuring safety and a proportionate, risk-based approach.

5.2.9 One comment related to the clarity of the consultation proposal with the respondent believing that some products were already exempt (e.g. flue liners) within the context of the consultation (i.e. buildings greater than 11m with external wall cladding systems attracting requirements for A1/A2 classification or the BS 8414 test alternative).

5.2.10 While one response felt the proposal removed any ambiguity and appeared to cover all possible penetrations to an external wall, another suggested that there are other features which may be better defined in an exclusion list i.e., more definition of exempted products and possible situation od use.

5.2.11 Clarity was also requested around very specific examples:

  • Further guidance around "membranes" would be helpful as this is a relatively broad term. Does this cover ethylene propylene diene terpolymer (EPDM) or other heavier waterproofing membranes in addition to breather and vapour control membranes.
  • One respondent felt that there were no grounds for solar shading products that extend and retract to meet the A1 or A2 classification criteria and that the components that assist in the operation of these products should be exempt as they are integral to the operation of the device e.g. nylon brushes, cabling to motors etc. The exemption list already includes fixings, seals and sealants and there should be greater clarity as to what components in a shading system are already exempt from BS EN 13501 classification A2-s1, d0 or A1.
  • A respondent also questioned why certain components enjoy an exemption when there are non-combustible alternatives e.g. PVC window frames versus aluminium window frames.

General Comments

5.2.12 There were a number of general comments relating to an expanded list including:

  • The need for any penetrations that do not meet the fire resistance of the external wall to at least meet the minimum fire resistance of the external cladding. This would apply to all service penetrations of any type or size.
  • There should be a caveat that every product needs to be fire risk assessed.
  • The precautionary principle should always operate as people's lives are at stake.

Disagreeing with Proposal

Weaken the System

5.2.13 Several respondents referred to the potential of an increase in the list of exemptions to lessen the chance of the product being able to act as A1 or A2 and hence, weakening the system. Related to this, it was suggested that penetrations through cladding should be fire resistant and that the use of the non-fire rated materials should be minimised.

Conditional Support

5.2.14 A few respondents drew attention to some research[13] which highlights the critical risk from fire of combustible vents, ducts, pipes etc. that breach the external cladding system. However, although disagreeing with the proposals, these respondents could offer conditional support for the addition of some exemptions where the cladding system comprises products classified as A2-s1, d0 or better and the penetrations are appropriately sleeved with cavity barriers, where a cavity is present. The exemptions include:

  • Cavity wall vents
  • Boiler condensate pipes
  • Drainage and overflow pipes
  • Ventilation extract ducts
  • Balanced flue liners etc.

General Comments

5.2.15 A number of general comments were also made including:

  • The majority of cases should be covered by the current list with a project specific assessment undertaken where additional penetrations are proposed.
  • The primary reason for exemptions should be where a product with the necessary reaction to fire classification is not available in the marketplace. Where a product is available, there should be no exemptions.
  • Such a list will never be complete and is open to abuse, particularly around definitions. For example, would a wooden panel with window and door openings cut into it be considered a "frame"? Are adhesives included only when they are also a sealant or could they count as a "fixing"? To address this issue it was suggested that it would be better to specify an overall limit on the amount of non-A1/A2 material that could be used.
  • A prescriptive approach is dangerous, open to interpretation, ineffective and requires constant review to allow for product developments, innovation and changes in construction methods.

5.2.16 One respondent also suggested adding some clarification to the listing of "insulation and water proofing materials used belowground level" by including "accepting their use to below the DPC rather than below ground level". This would avoid technical issues and was also raised by a respondent agreeing with the proposal (para 5.2.7 above).

Respondents who were Unsure about the Proposal

Qualified Support

5.2.17 Several respondents felt that there could be an expanded list of exemptions, but that there were qualifications to the list. Some of the qualifications included:

  • The list could include cavity wall vents, boiler condensate pipes, drainage and overflow pipes, but there was concern about ventilation extract ducts and balanced flue liners.
  • It depends on the situation in which the additional exemptions are used. For example, in the case of pipes, it would depend on the type (material) and the extent of the pipes. Full height plastic pipes within the external wall would be quite different to a pipe allowing venting through the wall. A respondent suggested that additional text could be added to enable any concerns to be raised regarding the type and extent of materials used. For example "Any penetration exceeding 10% of wall area which may adversely affect the fire performance of the external wall should be carefully considered".
  • The list does not recognise that the closures used are as important for building safety as the penetrations themselves.

Evidence Based

5.2.18 Several respondents felt that the list should only be expanded on the basis of suitable evidence that it will not contribute to the combustibility of the external wall. The more penetrations that are contained in the external wall, the greater the potential to compromise the cladding.

5.2.19 A few respondents suggested that any amendments should be advised in consultation with technical specialists. One respondent suggested that the list should be amended following Scottish Government engagement with relevant bodies (i.e. fire safety specialists, façade engineers and building standards) to determine the components that are not included in the exemptions list but where there is no product available that can achieve the A1 or A2 performance. This list should be subject to further review by a technical advisory group.

Not Exhaustive

5.2.20 A few respondents felt that the list can never be exhaustive and adding items appears reasonable. However, it should be made clear that each item within the construction of external walls should be considered in terms of the risk it poses on a case-by-case basis. One respondent also agreed that it is not possible to provide an exhaustive list but felt that the current list provides sufficient information.

General Points

5.2.21 As with points made by respondents above (paragraphs 5.2.7 and 5.2.17) it was suggested that the wording of the existing exemption relating to insulation and waterproofing be amended to "insulation and waterproofing materials used below DPC". The reason being that the DPC is often at least 150mmmm above ground level and more usually the DPC is at least 150mm above finished ground floor level, which is itself at least 150mm above external ground level. The commonly available A1 insulants are not suitable for use below DPC.

5.2.22 A number of other general points were made including:

  • Inconsistency about laminated glass. There is inconsistency with the current list of exemptions regarding curtain walling, specifically in relation to the treatment of glazing in spandrel areas. It was stated that laminated glass is unlikely to achieve class A1 or A2, but based on the current list it would still be permitted for use in curtain wall façade in all areas apart from spandrel areas.
  • For the existing exemptions for roofs and for thermal break materials, guidance would be helpful on upstands for roofing systems where the waterproofing system is dressed up the wall.
  • A few respondents made reference to the need for clarity on the definitions of balconies and terraces and requested that reference to BS 8579 "Guide to the design of balconies and terraces" is included in the Technical Handbook. One respondent stated that this British Standard defines a terrace as a roof, which has implications on the application of the second exemption listed in paragraph 5.1.1.
  • There is potential to "game" the system.

5.3 General Points

5.3.1 A concern was raised about the definition of solar shading provided in Section 2.7 of the Technical Handbooks. Solar shading is defined as "..devices attached to an external wall to reduce heat gain within a building by deflecting sunlight", but this definition was felt not to cover all the reasons for installing these products e.g. to reduced light ingress, privacy, to create usable outdoor space with protection from wind, rain and sun.



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